In vivo behavior of human muscle during isometric ramp contraction: A simultaneous EMG, MMG and ultrasonography investigation

The purpose of this study was to investigate the electromyography (EMG), mechanomyography (MMG), and the muscle architecture, i.e. cross-sectional area (CSA), amplitude versus torque relationships during voluntary isometric ramp contractions. The ultrasound images, EMG and MMG signals were simultaneously recorded from the rectus femoris (RF) muscle. A novel image processing algorithm was developed to automatically extract cross-sectional area (CSA) from ultrasound images. The root mean square (RMS) amplitudes of the EMG and MMG were computed on adjacent epochs in synchronization with the ultrasound images. Polynomial regression analyses indicated that both EMG and MMG amplitudes increased and CSA decreased curvilinearly with torque increment, and the change fashion of CSA was significantly different from those of EMG and MMG. The results demonstrated that the continuous change of CSA can provide useful information about muscle contractions. It may therefore complement EMG and MMG for studying muscle activation strategies.